ANSYS+GarField simulation of CRP induction efficiency, extraction - - PowerPoint PPT Presentation

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ANSYS+GarField simulation of CRP induction efficiency, extraction efficiency and effective gain.

P.COTTE, CEA Saclay 12 oct. 2017

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Content

• ANSYS geometry
• GarField input parameters and Microscopic

traking

• Definition and results of efficiencies and gain
• Conclusion

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LEM hole geometry

Base element in ANSYS simulation

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ANSYS Geometry : simple with symmetry conditions on borders

Grid ( considered as a plane)

Anode (considered as a plane)

Symmetry conditions on border give full hexagonal geometry

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GarField input parameters

• Pressure = 760 Torr
• Temperature = 87K
• 100 % Argon

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GarField simulation

• Electron starting point : just above liquid

(GarField does not simulate drift in liquid)

• Drift and avalanche method : microscopic

tracking, uses scattering rates and cross sections to simulate various kinds of collisions

• Also simulates photons emissions and their

ionising effect

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Example with anode=0V, LEM top=200V, LEM bottom = 3000V, Grid = 5500V

FR4 (=LEM) Extraction zone (gas) Induction zone Bottom copper Top copper liquid Starting point 1 2 3 4 5 Anode 1 1 2 1 2 3 3 4 4 5 5 Electron startpoints Electron endpoints

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Relevant values and their definition

• Induction efficiency = electron at anode / electrons exiting

amplification zone (main loss is on top copper)

• Extraction zone transparency =

electrons reaching amplification zone / electrons generated (main loss is on bottom copper) !!! only in gas !!!

• Total extraction efficiency =

transparency convoluted with liquid-gas extraction efficiency

• Effective gain = electrons at

anode / electrons generated Does not take charging up into account!

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Nominal voltage 2500V : Transp. = 0.7

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Nominal voltage 2500V : Extr. Eff. = 0.68 ± 0.07 → We should be able to divide extraction voltage by 2 without loosing efficiency ! Can it be checked in the 311 ? Total

D i d n

• t

t a k e i n t

• a

c c

• u

n t t h e f a c t t h a t v

• l

t a g e i n l i q u i d ! = v

• l

t a g e i n g a s

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Nominal voltage 2500V : Extr. Eff. = 0.58 ± 0.07 → Diminishing Grid-LEM voltage will significantly diminish efficiency.

Now it does : efficiency is a bit lower

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Optimal voltage 1000V

• Ind. Eff. = 0.7

Currently used voltage 200V

• Extr. Eff. = 0.32

(3L)

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Effective gain : simulation of 3L and comparison to measurements

Pressure set to 735 Torr to match experimental conditions Simulated gain ~ one third of measured gain => Measurement were done before charging up : should be equal to simulation Possible explanations :

• GarField microscopic tracking not

reliable for avalanche? → try other simulation methods (next slide)

• Should consider possible

photoelectric effects of UV going back to hit the grid, producing more electrons, increasing gain? → in progress

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3L simulation with Garfield’s MC method

Still a big discrepancy between data and simulation

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3L simulation with Garfield’s MC method

MC method Microscopic tracking method None of the two methods fit the data.

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Conclusion

• Extraction and induction efficiencies simulated,

can be added to simulation and reconstruction software

• Could check the total extraction zone efficiency

at lower extraction voltage on the 311

• Simulated gain is not coherent with

measurements, needs more investigations

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Induction efficiency when keeping the ratio of voltages induction/amplification constant

Simulation of Saclay’s HP Chamber when amplification voltage = 6 x induction voltage : Efficiency is constant